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Mahr (Digimatic, RS232C, Wireless FM Radio, Infrared and USB)[17]
Like dial calipers, the slide of a digital caliper can usually be locked using a lever or thumb-screw.
Some digital calipers contain a capacitive linear encoder. A pattern of bars is etched directly on the printed circuit board in
the slider. Under the scale of the caliper another printed circuit board also contains an etched pattern of lines. The
combination of these printed circuit boards forms two variable capacitors. The two capacitances are out of phase. As the
slider moves the capacitance changes in a linear fashion and in a repeating pattern. The circuitry built into the slider
counts the bars as the slider moves and does a linear interpolation based on the magnitudes of the capacitors to find the
precise position of the slider. Other digital calipers contain an inductive linear encoder, which allows robust performance
in the presence of contamination such as coolants.[18] Magnetic linear encoders are used in yet other digital calipers.
Micrometer caliper
A caliper using a calibrated screw for measurement, rather than a slide, is called an external micrometer caliper gauge, a
micrometer caliper or, more often, simply a micrometer. (Sometimes the term caliper, referring to any other type in this
article, is held in contradistinction to micrometer.)
Comparison
Each of the above types of calipers has its relative merits and faults.
Vernier calipers are rugged and have long lasting accuracy, are coolant proof, are not affected by magnetic fields, and are
largely shock proof. They may have both centimeter and inch scales. However, vernier calipers require good eyesight or a
magnifying glass to read and can be difficult to read from a distance or from awkward angles. It is relatively easy to
misread the last digit. In production environments, reading vernier calipers all day long is error-prone and is annoying to
the workers.
Dial calipers are comparatively easy to read, especially when seeking exact center by rocking and observing the needle
movement. They can be set to 0 at any point for comparisons. They are usually fairly susceptible to shock damage. They
are also very prone to getting dirt in the gears, which can cause accuracy problems.
Digital calipers switch easily between centimeter and inch systems.They can be set to 0 easily at any point with full count
in either direction, and can take measurements even if the display is completely hidden, either by using a "hold" key, or by
zeroing the display and closing the jaws, showing the correct measurement, but negative. They can be mechanically and
electronically fragile. Most also require batteries, and do not resist coolant well. They are also only moderately shockproof,
and can be vulnerable to dirt.
Calipers may read to a resolution of 0.01 mm or 0.0005 in, but accuracy may not be better than about ±0.02 mm or
0.001 in for 150 mm (6 in) calipers, and worse for longer ones.[19]
Use
A caliper must be properly applied against the part in order to take the desired measurement. For example, when
measuring the thickness of a plate a vernier caliper must be held at right angles to the piece. Some practice may be needed
to measure round or irregular objects correctly.
Accuracy of measurement when using a caliper is highly dependent on the skill of the operator. Regardless of type, a
caliper's jaws must be forced into contact with the part being measured. As both part and caliper are always to some extent
elastic, the amount of force used affects the indication. A consistent, firm touch is correct. Too much force results in an
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10/16/2019 Calipers - Wikipedia
underindication as part and tool distort; too
little force gives insufficient contact and an
overindication. This is a greater problem with a
caliper incorporating a wheel, which lends
mechanical advantage. This is especially the
case with digital calipers, calipers out of
adjustment, or calipers with a poor quality
beam.
Simple calipers are uncalibrated; the
measurement taken must be compared against a Using the vernier caliper
scale. Whether the scale is part of the caliper or
not, all analog calipers—verniers and dials—
require good eyesight in order to achieve the highest precision. Digital calipers have the advantage in this area.
Calibrated calipers may be mishandled, leading to loss of zero. When a calipers' jaws are fully closed, it should, of course,
indicate zero. If it does not, it must be recalibrated or repaired. A vernier caliper does not easily lose its calibration but a
sharp impact or accidental damage to the measuring surface in the caliper jaw can be significant enough to displace
zero.[20] Digital calipers have zero set buttons, for quick recalibration.
Vernier, dial and digital calipers can be used with accessories that extend their usefulness. Examples are a base that
extends their usefulness as a depth gauge and a jaw attachment that allows measuring the center distance between holes.
Since the 1970s a clever modification of the moveable jaw on the back side of any caliper allows for step or depth
measurements in addition to external caliper measurements, in similar fashion to a universal micrometer (e.g., Starrett
Mul-T-Anvil or Mitutoyo Uni-Mike).
Zero error
The method to use a vernier scale or caliper with zero error is to use the
formula "actual reading = main scale + vernier scale − (zero error)". Zero error
may arise due to knocks that affect the calibration at 0.00 mm when the jaws
are perfectly closed or just touching each other. Positive zero error refers to the
fact that when the jaws of the vernier caliper are just closed, the reading is a
positive reading away from the actual reading of 0.00 mm. If the reading is
0.10 mm, the zero error is referred to as +0.10 mm. Negative zero error refers When the jaws are closed and if the
to the fact that when the jaws of the vernier caliper are just closed, the reading reading is 0.10 mm, the zero error is
referred to as +0.10 mm. The
is a negative reading away from the actual reading of 0.00 mm. If the reading
method to use a vernier scale or
is −0.08 mm, the zero error is referred to as −0.08 mm. caliper with zero error is to use the
formula "(actual reading) = (main
See also scale) + (vernier scale) − (zero
error)", thus the actual reading is
Dial indicator 19.00 + 0.54 − (0.10) = 19.44 mm.
The resolution of the measurement,
Cruising rod
based on the width of the smallest
Lens clock
sub-interval, is ±0.02 mm.
References
1. Mensun Bound: The Giglio wreck: a wreck of the Archaic period (c. 600 BC) off the Tuscany island of Giglio, Hellenic
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